1. Field of the Invention
The present invention relates to a process for the production of spherical particles of ceramics. More particularly, the present invention relates to a novel process for the production of spherical, calcium phosphate-based ceramic particles which have a large diameter and a well defined roundness and therefore are particularly suitable as a filling material for osseous defects, as a carrier for drug delivery system and as a packing material for a liquid chromatography.
2. Description of Related Art
Calcium phosphate, especially hydroxylapatite has been found to be useful as a biomaterial such as osseous filling materials and as a packing material for a liquid chromatography. In fact, it has already been commercialized for these purposes.
Heretofore, hydroxylapatite used as a packing agent in a liquid chromatography has been comprised of irregularly shaped of particles, because those particles were produced by crushing. Recently, an improved packing agent using spherical hydroxylapatite has been developed. This improved packing agent exhibits a high resolution power and a good durability much superior to the resoltuion power and durability attainable by crushed hydroxylapatite particles. However, to attain a high flow rate in the liquid chromatography, it was necessary to increase the size of the particles of the filling agent.
Similarly, commercially available hydroxylapatite particles for use in implantation in vivo have been comprised of irregularly shaped particles because of the crushing employed in the production of those particles size. Particle of such particles has been about 100 .mu.m. Such hydroxylapatite particles can be introduced into osseous defects such as those encountered in various periodontal diseases. Hydroxylapatite particles can be filled in gaps between the dentition and the maxilla or mandibula to cover the gingiva, or, soft tissues. This generally accomplished in this manner is because soft tissues of a human body may be damaged by sharp edges of said particle,s.
Other typical production process for spherical particles including spherical hydroxylapatite particles are generally designated a spray drying process and a highspeed agitation granulation process.
The particles produced by the spray drying process have a shape similar to that of the complete spheres. Accordingly, heretofore, almost of the commercially available spherical hxdroxylapatite particles have been produced by this process. However, since resulting particle size is increased by increasing scale of the devices used, it is essential to use large-scale devices, especially if it is desired to provide spherical hydroxylapatite particles having a diameter of 10 .mu.m or more.
On the other hand, the high-speed agitation granulation process is characterized in that the particles of 100.mu.m or more can be produced by a relatively small device. However, this process is not suited to produce spherical hydroxylapatite particles. This is because of certain specific physical properties (mainly, water adsorption property) of the particles which prevent hydroxylapatite them from acquiring a complete spherical shape during such a process.